During the past years, the interest in using mobile and landline/wireline computing devices in day-to-day communications has increased. Desktop computers, workstations, and other wireline computers currently allow users to communicate, for example, via e-mail, video conferencing, and instant messaging (IM). Mobile devices, for example, mobile telephones, handheld computers, personal digital assistants (PDAs), etc. also allow the users to communicate via e-mail, video conferencing, IM, etc. Mobile telephones have conventionally served as voice communication devices, but through technological advancements they have recently proved to be effective devices for communicating data, graphics, etc. Wireless and landline technologies continue to merge into a more unified communication system, as user demand for seamless communications across different platforms increases.
As these technologies have advanced, applications which use them have likewise advanced to provide users with video streaming and other multimedia services. Such services require higher bandwidth channels between the network and the end user devices to avoid unacceptable latency, among other things. Thus, for example, each successive generation of wireless communication technology which is promulgated by the various standards bodies has typically enabled an end user device to acquire greater bandwidth channels for communication. Such systems are sometimes referred to as “wideband” or “broadband” systems to emphasize the increased bandwidth availability which they provide.
Devices employed in such systems use transceivers to transmit and receive broadband signals. The transmit portions of such devices typically employ an amplifier to amplify the signals prior to coupling the signals to one or more antennas for transmission. Such broadband amplification circuits include transistors. Transistors operating in an AC coupled environment typically include a bias network that decouples the power supply circuit from the signals that are being amplified by the transistor amplifier. Bias networks for relatively narrowband signals typically include a parallel inductor and capacitor arrangement so that they resonate at a frequency that is within the band of frequencies corresponding to the signal being amplified.
An example of a conventional amplifying circuit 100 is provided as FIG. 1. Therein, the matching circuit 102 is designed such that the impedance z4 seen by the matching circuit 102 at point 104 is Zload and the impedance z3 seen looking into the matching circuit at point 106 is the conjugate of ZSPC (i.e., Z*SPC), where ZSPC is the operating impedance of the transistor 108.
The signal to be amplified is injected into the amplifying circuit 100 at point 110. The transistor 108 amplifies the signal by transferring substantially all of the energy (minus losses) from node 112 to the node 104. The energy from the power supply (not shown) which is delivered to node 112 is in a different form than the amplified signal energy which is delivered to node 104, which energy conversion process is intrinsic to the transistor 108's amplification capability.
Also connected to the drain of the transistor 108 is a bias network 114. The drain bias network 114 includes at least one inductor 116 and at least one capacitor 118 connected to one another in parallel, and is used to prevent the signal amplified by the transistor 108 from leaking into the power supply circuits at node 112 and to allow energy to pass from power supply 112 to transistor amplifier 106. When the inductor 116 and the capacitor 118 are at resonance, then together they form a high impedance at the resonant frequency. If this resonant frequency corresponds to the frequency of the signal being amplified, then the amplified signal at node 106 will be substantially blocked from travelling to node 112, and thus onward into the power supply circuitry (not shown) which is connected to node 112.
A problem with the bias network 114 illustrated in FIG. 1 is that when the signal applied to node 110 for amplification contains a wide range of frequencies, then the high impedance associated with resonance of the LC circuit 116, 118 cannot be maintained over the entire range of frequencies associated with the amplified signal. Degradation of the signal at node 106 occurs and there may also be problems caused by signal leakage through node 112 to the power supply circuitry.
Accordingly, it would be desirable to provide amplifying circuits having bias networks and associated methods which avoid the afore-described problems and drawbacks.